Several non-human primate species are used as laboratory animals for research purposes. Non human primates represent a potential hazard for laboratory animal handlers as they exceed all other species in importance as potentiators of disease in laboratory personnel (Quist K.D., 1972). Hepatitis viruses cause some of the prevalent diseases in man which constitute an important public health problem. The first outbreak of the infection was related to non human primates and occurred in 1958-1960 in USA, with more then 200 human cases. Chimpanzee is the main species that has been implicated but others have also been involved. We report a case of seropositivity to HCV antigens in Macaca fascicularis using a third generation RIBA assay. The nature of reactivity of the positive samples could not be resolved as no animal in the breeder colony had been exposed to an HCV source. Furthermore, Macaca spp. did not appear to be a susceptible species in previous studies.